This invention relates generally to techniques for determining conditions of surfaces, and, more specifically, to doing so by measuring a characteristic of the reflectivity and/or emissivity of surfaces. An example application is the measurement of the thickness of a film on a substrate, such as a film that is formed or removed from a semiconductor wafer during the fabrication of integrated circuits. The thickness measurement is made either simultaneously with the film processing (in situ) or thereafter (in line). More specific applications include in situ measurements of the thickness of a film being reduced or removed by techniques such as wet etching, plasma etching, spin etching or chemical-mechanical-polishing (CMP).
As a result of the development of new semiconductor processing techniques and a steadily shrinking minimum semiconductor element size, a need exists to constantly improve techniques of monitoring and measuring the results of processing, and also to develop new ones. The trend is to make as many measurements of semiconductor wafers as possible in situ, which is usually more difficult to do than as a separate step after the processing. An example of one recent development is described in U.S. Pat. No. 5,769,540, wherein the reflectivity of a surface is measured, from which its emissivity and/or temperature can be determined without contacting the surface. The emissivity measurement is also usable to determine the thickness of a film carried by the substrate. These techniques are particularly useful for making in situ measurements during rapid thermal processing (RTP). Another development, described in U.S. Pat. No. 5,695,660, measures the thickness or level of planarization of both dielectric and metal layers in situ by optical or thermal techniques during etching or CMP, including making the measurements through the back side of the wafer. When applied to CMP, an optical signal communicates with a wafer being processed through an optical window provided in one of the moving elements such as the wafer carrier. In published international (PCT) application no. WO 97/25660, multiple sensors are carried by a moving component of a CMP machine, with a wireless communication of measurements and control signals provided between the sensors and a host control station. Other patent documents of interest include U.S. Pat. Nos. 5,138,149, 5,190,614, 5,166,525, 5,292,605, 5,308,447, 5,362,969, 5,717,608 and 5,786,886, and PCT publication no. WO93/25893. Each of the foregoing patent publications is from Luxtron Corporation of Santa Clara, Calif., the assignee hereof, and is incorporated herein in its entirety by this reference.
It is a principal object of the present invention to provide further improvements to methods and instruments for optically measuring characteristics of surfaces, such as surfaces of circuit structures partially formed on semiconductor wafers or flat panel displays.
It is a more specific object of the present invention to provide such further improvements to monitor the effects CMP processing.
It is another object of the present invention to provide improved optical methods and instruments for measuring the thickness of layers of dielectric, semiconductor or metal materials carried by a substrate.
It is a further object of the present invention to carry out the foregoing objects simultaneously with processing the surface or layer being monitored (in situ).
It is an even more specific object of the present invention to accurately measure the changing thickness of a layer carried by a substrate, such as a semiconductor wafer, while being processed (in situ) to increase or decrease the layer thickness.